This invention relates generally to interface shear transducers and more specifically to dynamic shear transducers that are insensitive to extraneous acceleration forces.
When a large structure is designed to be constructed either below ground level or above ground level with a substantial subsurface foundation structure, as for example are found in skyscrapers, all forces having an effect on the structure must be carefully and accurately evaluated. Subsurface forces may orginate in a number of ways including poor earthen materials that are inherently unstable or a mixture of earthen materials of unequal quality that would cause unequal forces on the structures. Additionally, some areas of the world are more prone to earthquakes and tremors than others causing potential hazardous forces on the structure. Similarly, floods or other unusual weather extremes could effect the strength and function of deeply seated foundations.
Another area of interest is in the aspect of structure survivability in the event of a severe shock as would accompany a nuclear explosion. Such information would be necessary, not only for the predictability of structure survival in the event of hostile explosions, but also where nuclear devices might be used for mining, oil exploration or construction.
Transducers for measuring the normal loading on a structure are well known in the art and have been used with a great deal of success for the purpose for which they were employed. However, currently there is no acceptable means of measuring and predicting the highly critical dynamic shear loading on a buried structure.
In the past, structure-media interface shear loading was implied or computed by coulomb models utilizing interface coefficient of friction factors, normal stress, and structure-media relative motions. Dynamic test results compared poorly with computed model results and as a result, a new and complex computer code was developed to provide the accurate results needed. With the new code, new means were needed to evaluate it, and in particular a means for measuring dynamic shear stress. Dynamic shear stress measurements require an instrument that is insensitive to acceleration forces and operates with nearly complete independence between orthogonal stress axes.
Various dynamic parameters measured to evaluate a structure include velocity, acceleration and displacement. Other parameters included in the calculations include; soil stress, blast pressure (if any), shear and interface normal stress.
This invention provides a means for solving the difficulties found in this art in the past.